1. Field
Example embodiments relate to semiconductor devices, and more particularly, to high electron mobility transistors (HEMTs).
2. Description of the Related Art
Various power conversion systems include devices for controlling the flow of current and switching current on or off, that is, power devices. The efficiency of power conversion systems may depend on the efficiency of power devices.
As power devices, power metal-oxide-semiconductor field-effect transistors (MOSFETs) using silicon (Si) or power insulated gate bipolar transistors (IGBTs) using Si have been mainly used. However, it is difficult to improve the efficiency of power devices using Si due to limitations in physical properties of Si and manufacturing processes. Attempts to improve conversion efficiency by applying group III-V compound semiconductors to power devices have been made. In particular, high electron mobility transistors (HEMTs) using a heterojunction between compound semiconductors have attracted attention.
A HEMT includes semiconductor layers having different electrical polarization characteristics. In the HEMT, a first semiconductor layer having a relatively high polarizability may induce a two-dimensional electron gas (2DEG) in a second semiconductor layer attached to the first semiconductor layer, and the 2DEG may have a very high electron mobility.
When a HEMT is normally on, current flows between a drain electrode and a source electrode due to a low resistance when a gate voltage is 0 V, current and power may be consumed, and a negative voltage has to be applied to a gate electrode in order to cut off the current between the drain electrode and the source electrode. A HEMT may be normally off so that a current between a drain electrode and a source electrode is cut off when a gate voltage is 0 V. A HEMT that may be normally off by adding a depletion-forming layer has recently been studied.